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IC 9126 



Bureau of Mines Information Circular/1987 



Hose Safety During High-Pressure 
Water-Jet Cutting 



By C. D. Taylor, J. L. Thompson, H. J. Handewith, 
and E. D. Thimons 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 9126 



Hose Safety During High-Pressure 
Water-Jet Cutting^ 



By C. D. Taylor, J. L. Thompson, H. J. Handewith, 
and E. D. Thimons 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 




77Y^ 



Library of Congress Cataloging- in Publication Data: 



Hose safety during high-pressure water-jet cutting. 

(Information circular ; 9126) 
Includes bibliographical references. 
Supt. of Docs, no.: I 28.27: 9126. 



1. Mining machinery -Safety measures. 2. Water-jet -Safety measures. 3. Jet- 
cutting -Safety measures. 4. Hose-Safety measures. I. Taylor, Charles D. (Charles 
Darrell), 1946- . II. Title. III. Series: Information circular (United States. Bureau of 
Mines) ; 9126. 



£N295#* [TN345] 



622 s 



[622'.8] 



86-600354 



CONTENTS 

.*.'!•. Pa S e 

Abstract 1 

Introduction • 2 

Hose selection • 3 

Test procedure 3 

Results 5 

Discussion 7 

Use of outer sleeves 7 

Hose coupling construction 7 

Location of hoses and couplings 7 

Noncatas trophic failure 7 

Catastrophic failure 9 

Actual and rated burst and working pressures 9 

Conclusions and recommendations 9 

ILLUSTRATIONS 

1. High-pressure hose 3 

2. Hose containment area 4 

3. Intensifier used for burst tests 4 

4. Noncatastrophic hose failure 5 

5. Catastrophic hose failure 6 

6. Cross section of typical coupling construction 8 

7. Fitting failure 8 

TABLES 

1. High-pressure hoses tested 3 

2. Fatigue test results 5 

3. Burst test results 6 





UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


c/min 


cycle per minute pet percent 


in 


inch psi pound per square inch 


mm 


millimeter 



HOSE SAFETY DURING HIGH-PRESSURE WATER-JET CUTTING 



By C. D. Taylor, 1 J. L. Thompson, 2 H. J. Handewith, 3 and E. D. Thimons 4 



ABSTRACT 

Flexible hoses with rated working pressures up to 40,000 psi are used 
when high-pressure water jets are employed to cut rock or improve the 
performance of mining machines. Hose failures at such high pressures 
can result in serious injuries to workers. 

The Bureau of Mines used fatigue and burst tests to investigate the 
failure modes of high-pressure hoses at their rated working and burst 
pressures. Fatigue failure, at rated working pressures, occurred when 
the inner liner of the high-pressure hose broke, allowing water to seep 
through the wire wrapping, although the reinforcement wires did not 
break. At the burst pressure, all hoses failed catastrophically when 
the reinforcement wires broke. Low-pressure hoses placed over the high- 
pressure hoses for safety failed to contain water released by cata- 
strophic failure. 



' Industrial hygienist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 

o . . . . . 

^Project engineer, Boeing Services International, Pittsburgh, PA. 

^Marketing manager, Advanced Mining and Construction Corp. (ADMAC), Kent, WA. 

^Supervisory physical scientist, Pittsburgh Research Center. 



INTRODUCTION 



The use of high-pressure water to cut 
rock or assist in the mechanical cutting 
of rock is being evaluated by the Bureau 
of Mines and others. 5 Water jet cutting 
uses solid or pulsed streams of high- 
pressure water which, upon impact with 
rock, have sufficient energy to cut and/ 
or fracture the material. For water- 
jet-assisted cutting, the high-pressure 
water is directed through spray nozzles 
located in front of each cutting bit on 
the miner drum. The spray nozzle pro- 
duces a solid stream of water that im- 
pinges on the rock within 5 mm ahead of 
the cutting bit. The added energy sup- 
plied by the water improves rock cutting 
and bit wear and reduces dust generation 
and fines. 

High water pressures for water-jet 
cutting are produced by a pressure- 
compensated piston pump or by an intensi- 
fier. Water is carried to the spray noz- 
zles through hard piping or specially 
constructed flexible hose. In some 
cases, it is necessary to route the flex- 
ible hose through areas where miners must 
work, which could present a safety hazard 
if the hose ruptures. 

The use of high-pressure water during 
mining shows considerable promise; how- 
ever, the associated safety hazards have 
not been fully investigated. Many hose 
safety standards (e.g., for hydraulic oil 
hoses) are written for applications where 
the hose pressure does not exceed 10,000 
psi. For water jet cutting, water pres- 
sures of 30,000 psi or greater may be re- 
quired. Therefore, safety standards that 
apply to hoses for hydraulic fluids will 
not necessarily protect workers using 
high-pressure water hoses. 

A jet of high-pressure water at 2,000 
psi (0.006-in-diam orifice) can penetrate 
through 60 mm of human tissue. ^ Rupture 

^Taylor, CD., and R.J. Evans (comp. ) . 
Water-Jet-Assisted Cutting. Proceedings: 
Bureau of Mines Open Industry Meeting, 
Pittsburgh, PA, June 21, 1984. BuMines 
IC 9045, 1985, 86 pp. 



of a high-pressure hose can result in a 
brief but potentially dangerous stream 
of high-pressure water that could cause 
serious injury to workers. 

Adequate safety standards must be a 
primary consideration when using high- 
pressure-water underground, because water 
pressures up to 40,000 psi are required 
for some mining applications. 

The operating characteristics of hoses 
are routinely evaluated by the manufac- 
turers. However, the testing procedures 
used have not been published, and the 
testing procedures vary among the manu- 
facturers. Hose testing procedures that 
have been published by several different 
organizations are written for specific 
types of hose and are not applicable for 
high-pressure water hose. 

The objective of this study was to in- 
vestigate the failure modes of typical 
high-pressure hoses and determine what 
safety hazards hose failures could pre- 
sent to a worker. Hose failure due to 
fatigue was studied by repeatedly cycling 
the water pressure up to the rated work- 
ing pressure. For burst testing, the 
pressure was gradually increased until 
failure occurred. Protective sleeves 
consisting of sections of hose with lower 
pressure ratings were placed over the 
high-pressure hoses. Following failure 
of the inner hose, the sleeve was exam- 
ined to determine if it had ruptured. A 
rupture in the sleeve would allow high- 
pressure water to escape from the annular 
area between the two hoses. Manufactur- 
ers' rated minimum burst pressures were 
compared with the actual burst pressures 
from the Bureau's tests. 

^Ward, G. M. Safety Considerations 
Arising From Operational Experience With 
High Pressure Jet Cleaning. Paper F-1 in 
First International Symposium on Jet Cut- 
ting Technology (Proc. Symp. Univ. War- 
wick, United Kingdom, Apr. 5-7, 1972). 
BHRA Fluid Eng. , Cranfield, Bedford, 
England 1972, pp. F1-F34. 



HOSE SELECTION 



Most available high-pressure hoses have 
a maximum inside diameter (ID) of 0.20 in 
and a rated working pressure of 30,000 to 
35,000 psi. The manufacturers of the 
hose samples used established the rated 
working pressure at either 50 or 25 pet 
of the minimum rated burst pressure. 
Other manufacturers state that highly 
pressurized hoses can be safely used at 
75 pet of the minimum rated burst pres- 
sure if a lower pressure rated sleeve is 
loosely fitted over the higher pressure 
hose. 

Samples of high-pressure hose, 18 and 
36 in long, from three manufacturers, 
were tested. Characteristics of each 
hose type are given in table 1. The mini- 
mum rated burst and working pressure val- 
ues given were provided by the hose manu- 
facturers. End fittings were provided 
and installed by the manufacturers. 



TABLE 1. - High-pressure hoses tested 



Hose type 


Hose ID, 
in 


Min rated pressure, 
psi 




Burst 


Working 


A 


0.20 
.25 
.20 


72,500 
40,000 
62,600 


36,250 


B 


10,000 




31,300 



Type A and B hoses had polymer inner lin- 
ers, and type C had a rubber inner liner. 
Surrounding the inner liner were six lay- 
ers of counterwound stainless steel 
wires (fig. 1). The wires were covered 
with either plastic or fabric. The hose 
used as the protective sleeve had a 3/4- 
in ID, a rated burst pressure of 5,000 
psi, and a rated working pressure of 
1,250 psi. The sleeve had a polymer in- 
ner liner reinforced with double-braided 
polyester cords covered with plastic. 



TEST PROCEDURE 



For each fatigue test, a 36-in length 
of either hose type A or B was connected 
to the test fixture. Thirty-six-inch 
lengths of type C hose were not avail- 
able, and therefore this hose was not 
fatigue tested. Fatigue testing con- 
sisted of cycling the pressure in the 
hose from atmospheric pressure to the 
rated working pressure at 20 c/min for a 



minimum of 2,000 cycles unless failure 
occurred first. The fatigue tests were 
intended to simulate day-to-day usage. 
Hose samples that did not fail during 
fatigue testing were placed on the burst 
test apparatus to determine if the fa- 
tigue testing had weakened the hose caus- 
ing it to burst at a lower pressure. 



Hose 
covering 



Stainless steel 
reinforcement wire 
a 



Inner liner 



T r / "" 'f2sY,t;, ;.y,y.yj 



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L 



Scale, in 
FIGURE 1.— High-pressure hose showing layers of reinforcement wires. 



For burst testing, the Bureau used a 
hose burst test fixture that was designed 
and fabricated by a commercial firm for 
routine quality testing of high-pressure 
water hoses. The test unit consists of 
hinged steel channel sections locked to- 
gether to create a safe pressure contain- 
ment area for bursting hoses. An insert 
of clear rigid plastic in the top channel 
facilitates viewing (fig. 2). The high- 
pressure water is generated by an inten- 
sifier with a 47:1 water-to-oil pressure 
ratio (fig. 3). For safety, the intensi- 
fier is located at the end of the test 
unit, inside a steel cylinder. 

Fifteen new 18-in-long hose samples and 
seven 36-in-long samples that did not 



burst during fatigue testing were burst 
tested. For each burst test, the hose 
sample was placed in a test box and the 
coupling attached to the fitting leading 
to the pressure intensifier. The other 
end of the hose was connected to an ele- 
vated reservoir that displaced all air in 
the test sample and in the plumbing con- 
nected to the intensifier. When all air 
was eliminated from the system, the res- 
ervoir feed line was disconnected from 
the sample hose and replaced with an end 
cap. After the hydraulic system was 
pressurized, the intensifier cylinder 
raised the water pressure until the hose 
failed. Burst pressures were recorded on 
maximum-reading hydraulic gauges. 



Viewing 
window 





FIGURE 2.— Hose containment area. 



FIGURE 3.— Intensifier used for burst tests. 



RESULTS 



The fatigue test results are shown in 
table 2. The location where failure oc- 
curred in the hose is specified as 
"middle" or "end." "Middle" failures 
refers to failures that occurred at a 
distance greater than 2-1/2 times the 
hose outside diameter (OD) from the end 
fitting, while "end" failures occurred 
less than 2-1/2 times the hose OD from 
the end fitting. All failures during 
fatigue testing resulted in ballooning of 
the outer hose jacket (fig. 4) and were 
noncatastrophic (i.e., the water pressure 
was released slowly). In some cases, 
however, the ballooning was not local- 
ized, which made it difficult to locate 
the actual point of failure. None of the 

TABLE 2. - Fatigue test results 



Fatigue test 



1.. 
2.. 
3.. 
4.. 
5.. 
6.. 
7.. 
8., 
9.. 
10. 
11. 
12. 
13. 
14. 
15. 



Hose 


Cycles 


Failure 


type 


run 


location 


A 


4,000 


None. 


A 


2,300 


Do. 


A 


2,500 


Do. 


A 


4,000 


Do. 


B 


2,000 


Do. 


B 


4,000 


Do. 


B 


6,000 


Do. 


A 


2,550 


Middle. 


A 


9,040 


Do. 


A 


8,727 


Do. 


A 


3,200 


Do. 


A 


10,717 


Do. 


A 


1,378 


Do. 


A 


2,200 


End. 


A 


3,198 


Middle. 



sleeves placed over the high-pressure 
hoses during the fatigue tests failed. 

Results from the burst testing are 
given in table 3. For each test, the 
actual pressure at which the hose sample 
failed is given, and the burst pressure 
is also expressed as a percentage of the 
rated burst pressure. Table 3 also gives 
the number of fatigue cycles for the 
seven hose samples that did not fail dur- 
ing the fatigue tests and were sub- 
sequently burst tested. 

In addition to middle and end failures, 
fitting failures also occurred during the 
burst tests (table 3). Fitting failures 
resulted in extrusion of material through 
the fitting weep holes or fracture of the 
fitting. 

All failures during burst testing were 
catastrophic, producing a sudden and 
violent release of water preceded by 
breaking of the stainless steel rein- 
forcement wires surrounding the inner 
lining (fig. 5). Two of the 22 cata- 
strophic failures occurred at pressures 
significantly lower than the manufact- 
urer's rated minimum burst pressure 
(tests 11 and 12). 

For 11 of the burst tests, sleeves were 
placed over the high-pressure hose. The 
results in table 3 show that the sleeve 
failed in 7 of these 11 tests. Three of 
the sleeves were undamaged because the 
hose failure occurred in the fitting, 
beyond the sleeve length. Only one other 
sleeve did not fail (test 11); however, 
the inner hose broke catastrophically at 






L 



Scale, in 



FIGURE 4.— Noncatastrophic hose failure. 



TABLE 3. - Burst test results 



Burst 
test 



Hose 
type 



Burst pressure 



Actual, 

J3SJL 



Pet of 
rated 2 



Fatigue 
test cycles 
,1 



run 1 



Failure 
location 



Sleeve test 
failure 3 



1.. 
2.. 
3.. 
4.. 
5.. 
6.. 
7.. 
8.. 
9.. 
10. 
11. 
12. 
13. 
14. 
15. 
16, 
17. 
18. 
19. 
20. 
21. 
22. 



A 
A 
A 
A 
A 
A 
A 
A 
A 
A 
A 
A 
A 
A 
A 
A 
B 
B 
B 
C 
C 
C 



133,000 
128,000 
94,000 
94,000 
126,900 
82,250 
89,300 
85,775 
84,600 
84,600 
54,050 
42,300 
103,400 
103,400 
82,250 
82,250 
75,200 
75,200 
63,450 
63,450 
74,025 
75,200 



183 
177 
130 
130 
175 
113 
123 
118 
117 
117 
75 
58 
144 
144 
113 
113 
188 
188 
159 
101 
118 
120 



























4,000 

2,300 

2,500 

4,000 

2,000 

4,000 

6,000 









Fitting 
• .do. • • 
• • do* • • 
• • do* • • 

End 

Middle. 
• • do* • • 

End 

Middle. 
. . do. . . 
. .do. . . 
. . do. . . 
Fitting 
. . do. . . 
Middle. 
. . do. . . 

End 

Fitting 
. . do. . . 
. . do. . . 

End 

Middle. 



NAp. 

NAp. 

NAp. 

NAp. 

NAp. 

Yes. 

Yes. 

Yes. 

Yes. 

Yes. 

No. 

Yes. 

No. 

No. 

NAp. 

Yes. 

NAp. 

NAp. 

No. 

NAp. 

NAp. 

NAp. 



dumber of fatigue test cycles prior to burst tests. 
2 From table 1. 

3 Yes = sleeve penetrated; No - sleeve not penetrated; NAp = not ap- 
plicable, no sleeve test. 








Scale, in 



FIGURE 5.— Catastrophic hose failure. 



a pressure lower than the actual burst 
pressure for most of the hoses tested, so 
a lower pressure spray was directed at 
the inner wall of the sleeve. Every 



sleeve subjected to a catastrophic fail- 
ure at or above the rated burst pressure 
failed to contain the water. 



DISCUSSION 



USE OF OUTER SLEEVES 

Following catastrophic failure of the 
high-pressure hose, the escaping water 
impinged on the inner surface of the 
sleeve. The sleeve did not fail due to 
the buildup of static fluid pressure in 
the annular space between the hoses, but 
because the sudden release of high-pres- 
sure water from the inner hose impinged 
on a small area of the sleeve with suf- 
ficient force to penetrate the sleeve 
material. During fatigue testing, the 
sleeves were not penetrated by any of the 
noncatastrophic failures. In all cases, 
the pressure of the water escaping from 
the high-pressure inner hose in the fa- 
tigue tests was lower than during cata- 
strophic failure in the burst tests. 

Further studies are needed to ascertain 
the feasibility of using a lower pressure 
outer hose to contain the catastrophic 
failure of a high-pressure hose. Only 
one type of hose was tested for use as an 
outer covering during these tests. Other 
types of hose (e.g. , hoses having varying 
wall thickness and construction) should 
be tested to determine their ability to 
contala high-pressure water from a rup- 
tured inner hose. 

In this study it was not possible to 
determine the annular distance between 
the inner and outer hoses at the point of 
inner hose failure, or whether the two 
hoses were actually in contact. Even a 
short annular distance may be sufficient 
to allow the energy released from the in- 
ner hose to dissipate, resulting in 
less water pressure on the sleeve. Annu- 
lar distance and other factors affecting 
outer sleeve performance should be stud- 
ied further. 

HOSE COUPLING CONSTRUCTION 

The construction of the hose couplings 
is important when considering the safety 
of the high-pressure flexible hoses. The 



coupling may contribute to hose failure 
by weakening the reinforcement wires when 
the coupling is crimped in place (fig. 
6). Coupling designs should be studied 
to determine hose integrity as a func- 
tion of coupling type and installation 
technique. 

In some tests the metal coupling split 
along the longitudinal axis (fig. 7). It 
is not known if this type of fitting 
failure was preceded by catastrophic 
failure of the hose inside the fitting. 
None of the couplings that failed by 
splitting had weep holes. When fittings 
with weep holes failed, failure occurred 
inside the coupling with sufficient force 
to extrude part of the liner through the 
weep hole. In these cases, release of 
pressure through the weep hole prevented 
rupture of the coupling or failure of the 
hose elsewhere. 

LOCATION OF HOSES AND COUPLINGS 

Obviously, the hazards associated with 
high-pressure water are much greater if 
high-pressure hoses are routed through 
areas where miners must work. In one 
test, a coupling broke away from the 
hose, but in no test was whipping of the 
hose material observed. All hose should 
be routed along equipment structures in 
such a way as to provide maximum protec- 
tion of the operator and other workers. 

NONCATASTROPHIC FAILURE 

Noncatastrophic failure was the result 
of hose fatigue, which in these tests was 
induced by periodic cycling of the water 
pressure between atmospheric and working 
pressures. Noncatastrophic failures 
resulted in the slow release of water at 
pressures too low to cause rupture of the 
reinforcement wires or penetration of the 
outer hose. There was no indication from 
these tests that inducing hose fatigue 
failures resulted in a weakening of the 





1_ 



Layered 
reinforcement 



wires 



Polymer liner 




Inner coupling 



Outer coupling 



% 



I 



Scale, in 

FIGURE 6.— Cross section of typical coupling construction. 




linn 



mttjmmm g^ 







Scale, in 



FIGURE 7.— Fitting failure (longitudinal split). 



reinforcement wires. Because water is 
released at a lower pressure, the safety 
hazard to workers when noncatastrophic 
failure occurs is not great. 

CATASTROPHIC FAILURE 



pressure. Pressure relief valves that 
release water in a safe location should 
be used. 

ACTUAL AND RATED BURST 
AND WORKING PRESSURES 



The results of these tests indicate 
that catastrophic failure of high- 
pressure hose can occur if the pressure 
rises above the rated working pressure. 
The potential for dangerous failures is 
greatly reduced if pressures are main- 
tained at or below the working pressure. 
During fatigue testing, the rated working 
pressure was not exceeded and no cata- 
strophic failures occurred. Safeguards 
should be considered to prevent hoses 
from accidental or intentional pres- 
surization above the rated working 



In most cases, the actual burst pres- 
sure exceeded the rated minimum burst 
pressure assigned by the hose manufac- 
turer. The method of assigning the rated 
working pressure varied with the manufac- 
turer. For the hoses tested, the rated 
working pressure was either 50 or 25 pet 
of the minimum burst pressure. While 
most of the catastrophic hose failures 
occurred at pressures much greater than 
the rated minimum burst pressure, two 
such failures occurred at 58 and 74 pet 
of the rated minimum burst pressure. 



CONCLUSIONS AND RECOMMENDATIONS 



All of the hoses that failed during the 
fatigue tests failed in a noncatastrophic 
manner; the inner liner broke, and water 
was forced slowly through the wire rein- 
forcement, causing a bubble to form in- 
side the plastic outer covering (fig. 4). 
Post-test inspections of these hoses 
showed that the wire reinforcement was 
not damaged, but that the inner liner had 
failed. Hoses that did not fail during 
fatigue testing were subsequently burst 
tested. These hose samples did not show 
significant reduction in actual burst 
pressures, suggesting that fatigue test- 
ing did not weaken the wire reinforce- 
ment. 

All burst tests resulted in catas- 
trophic hose failure, causing a sudden 
release of water and rupture of the hose 
reinforcement wires. Except for failures 
that occurred within the fitting, the 
broken wires formed a crater on the sur- 
face of the hose (fig. 5). 

Variations exist in the methods em- 
ployed by hose manufacturers to cate hose 
working pressures. A uniform method 



should be adopted for rating high- 
pressure hose used for water-jet and 
water-jet-assisted cutting applications. 
First, the method of establishing the 
rated minimum burst pressure should be 
standardized. Second, the same safety 
factor should be used for determining the 
working pressure of all hoses used to 
carry high-pressure water. 

Evaluation of the sleeve containment 
tests indicates that a sleeve covering 
the high-pressure hose may not provide 
additional protection to a worker in the 
event of a catastrophic hose failure. 
The containment sleeve was penetrated by 
the high-pressure water stream in seven 
of eight burst pressure tests in which 
the inner hose failure occurred at a lo- 
cation covered by the sleeve. No sleeve 
failures resulted during fatigue testing 
when the inner hose failed noncatastroph- 
ically. Further testing is needed to de- 
termine if sleeve materials other than 
the one type tested will provide protec- 
tion in the event of a catastrophic 
failure. 



15087 211 



U.S. GOVERNMENT PRINTING OFFICE: 1 987 60501 7/6001 3 



INT.-BU.OF MINES,PGH.,PA. 28410 



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Bureau of Mines— Prod, and Dmtr. 
Cochrane Mill Road 
P.O. Box 18070 
Pittsburgh. Pa. 15236 



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